Add unit tests for custom charm functionality

charm/tests/unit/test_charm.py

@@ -0,0 +1,100 @@
+# Copyright 2026 Canonical Ltd.
+# See LICENSE file for licensing details.
+
+"""Unit tests for the cs.canonical.com charm's custom functionality.
+
+Tests cover: workload version setting on pebble-ready and update-status.
+"""
+
+import os
+import pathlib
+import sys
+import unittest.mock
+
+import ops
+import yaml
+
+mock_paas = unittest.mock.MagicMock()
+mock_paas.flask.Charm = ops.CharmBase
+sys.modules["paas_charm"] = mock_paas
+sys.modules["paas_charm.flask"] = mock_paas.flask
+
+CHARM_DIR = pathlib.Path(__file__).parents[2]
+sys.path.insert(0, str(CHARM_DIR / "src"))
+
+os.environ["SCENARIO_SKIP_CONSISTENCY_CHECKS"] = "1"
+
+import charm  # noqa: E402
+import ops.testing  # noqa: E402
+
+# Load and merge metadata for the test subclass.
+_raw = yaml.safe_load((CHARM_DIR / "charmcraft.yaml").read_text())
+_FLASK_EXT_META = {
+    "assumes": ["k8s-api"],
+    "containers": {"flask-app": {"resource": "flask-app-image"}},
+    "peers": {"secret-storage": {"interface": "secret-storage"}},
+    "provides": {
+        "grafana-dashboard": {"interface": "grafana_dashboard"},
+        "metrics-endpoint": {"interface": "prometheus_scrape"},
+    },
+    "requires": {
+        "ingress": {"interface": "ingress", "limit": 1},
+        "logging": {"interface": "loki_push_api"},
+    },
+    "resources": {
+        "flask-app-image": {"description": "flask application image.", "type": "oci-image"}
+    },
+}
+_META = {k: v for k, v in _raw.items() if k not in ("config", "actions", "extensions")}
+for key, ext_value in _FLASK_EXT_META.items():
+    if key not in _META:
+        _META[key] = ext_value
+    elif isinstance(ext_value, dict) and isinstance(_META[key], dict):
+        merged = dict(ext_value)
+        merged.update(_META[key])
+        _META[key] = merged
+_CONFIG = _raw.get("config")
+_ACTIONS = _raw.get("actions")
+
+
+class _TestCsCharm(charm.CsCanonicalComCharm):
+    """Register observers that the real parent class would provide."""
+
+    def __init__(self, *args):
+        super().__init__(*args)
+        self.framework.observe(
+            self.on.flask_app_pebble_ready, self._on_pebble_ready
+        )
+        self.framework.observe(
+            self.on.update_status, self._on_update_status
+        )
+
+
+class TestWorkloadVersion:
+    """Test workload version is set on appropriate events."""
+
+    def test_pebble_ready_sets_version(self):
+        """On pebble-ready, workload version is set to VERSION constant."""
+        ctx = ops.testing.Context(
+            _TestCsCharm, meta=_META, config=_CONFIG, actions=_ACTIONS,
+        )
+        container = ops.testing.Container("flask-app", can_connect=True)
+        state = ops.testing.State(containers={container}, leader=True)
+
+        state_out = ctx.run(ctx.on.pebble_ready(container), state)
+        assert state_out.workload_version == charm.VERSION
+
+    def test_update_status_sets_version(self):
+        """On update-status, workload version is refreshed."""
+        ctx = ops.testing.Context(
+            _TestCsCharm, meta=_META, config=_CONFIG, actions=_ACTIONS,
+        )
+        container = ops.testing.Container("flask-app", can_connect=True)
+        state = ops.testing.State(containers={container}, leader=True)
+
+        state_out = ctx.run(ctx.on.update_status(), state)
+        assert state_out.workload_version == charm.VERSION
+
+    def test_version_constant_is_correct(self):
+        """VERSION constant has the expected value."""
+        assert charm.VERSION == "1.8.1"